Abstract
In this work, we theoretically analyze a gold (Au) core within silver (Ag) shell (Au@Ag) nanorod dimer biosensor for label-free molecule detection. The incident light on an Au@Ag nanorod strongly couples to localized surface plasmon modes, especially around the tip region. The field enhancement around the tip of a nanorod or between the tips of two longitudinally aligned nanorods as in a dimer can be exploited for sensitive detection of biomolecules. We derive analytical expressions for the interactions of an Au@Ag nanorod dimer with the incident light. We also study the detail dynamics of an Au@Ag nanorod dimer with the incident light computationally using finite difference time domain (FDTD) technique when core-shell ratio, relative position of the nanorods, and angle of incidence of light change. We find that the results obtained using the developed analytical model match well with that obtained using FDTD simulations. Additionally, we investigate the sensitivity of the Au@Ag nanorod dimer, i.e., shift in the resonance wavelength, when a target biomolecule such as lysozyme (Lys), human serum albumin (HSA), anti-biotin (Abn), human catalase (CAT), and human fibrinogen (Fb) protein molecules are attached to the tips of the nanorods.
Highlights
Last few decades have witnessed an increasing research interest in noble metal nanoparticles— especially gold (Au)[1,2] and silver (Ag)[3,4] nanoparticles—due to their interesting optical properties
We investigate the sensitivity of Au-core within Ag-shell (Au@Ag) nanorod dimers for single biomolecule detection for lysozyme (Lys), human serum albumin (HSA), anti-biotin (Abn), human catalase (CAT), and human fibrinogen (Fb) protein molecules
We find that the change in localized surface plasmon resonance (LSPR) shift decreases to ∼0.73% when the noise HSA molecule is located at 4 nm
Summary
Last few decades have witnessed an increasing research interest in noble metal nanoparticles— especially gold (Au)[1,2] and silver (Ag)[3,4] nanoparticles—due to their interesting optical properties. It is important to theoretically model the dynamics for an in-depth understanding so that plasmonic properties of nanoparticles can be exploited and optimized for sensing of biomolecules.[17] Gold nanorods have been extensively studied to understand the coupling of incident light to plasmonic modes and the change in plasmonic resonances when protein molecules attach to them.[17,18,19] The interaction of incident light with single nanorod homodimers has been studied theoretically, including the change in LSPR due to the angle between excitation polarization and the dimer orientation.[20,21] Recently, localized field enhancement due to plasmonic mode excitation has been studied in Au-Ag nanorod heterodimers.[22] a detail theoretical analysis of Au@Ag nanorod dimer sensors including understanding of complex physics when biomolecules attach to the tips is still lacking. We investigate the sensitivity of Au@Ag nanorod dimers for single biomolecule detection for lysozyme (Lys), human serum albumin (HSA), anti-biotin (Abn), human catalase (CAT), and human fibrinogen (Fb) protein molecules
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